In testimony to a Congressional committee last Wednesday, a FERC staffer downplayed the assertion made in a recent General Accounting Office (GAO) report that there is disagreement among experts over the distance at which a fire from a liquefied natural gas (LNG) spill would pose a threat of burns.

J. Mark Robinson, director of the Federal Energy Regulatory Commission’s (FERC) office of energy projects, testified before the House Homeland Security Committee on LNG tanker security. He told the committee that the GAO report “Public Safety Consequences of a Terrorist Attack on a Tanker Carrying Liquefied Natural Gas Need Clarification” mischaracterized expert opinion on a 2004 study by the Department of Energy’s (DOE) Sandia National Laboratories (see NGI, March 19). That study concluded that the most likely distance for a burn from LNG-generated heat is one mile, the same guideline used by FERC and the U.S. Coast Guard.

GAO reviewed six studies of LNG hazards, including Sandia’s, and interviewed 19 LNG hazard analysis experts and found the expert opinion on the distance at which 30 seconds of exposure to LNG-generated heat could cause burns varied from less than one-third of a mile to 1 1/4 mile.

“As stated in the 2004 Sandia report, the most significant impacts to public safety and property exist within approximately 500 meters (1,640 feet) of a spill due to thermal hazards from a fire, with lower public health and safety impacts beyond 1,600 meters (approximately 1 mile),” Robinson testified. “We believe the Sandia report and FERC’s site-specific analysis are a reasonable and conservative basis to examine potential impacts from an LNG tanker fire.

“The GAO study reports four experts thought the Sandia distance calculations were ‘too conservative’; four thought ‘not conservative enough’; and seven thought ‘about right.’ Although the report characterizes this as disagreement, the majority of the panel (11 of 15) responded that the calculations were either accurate or overly conservative.”

Four of the 19 experts did not respond to the question.

The GAO report concluded that explosions are not likely to occur in the wake of an LNG spill unless vapors are in a confined space. Some hazards, such as freeze burns and asphyxiation, are not a hazard to the public.

Robinson testified that FERC staff “generally agrees” with the material in the GAO report, but further explanation of some items is necessary.

“For instance, the report mentions that an LNG vapor cloud is visible, but natural gas vapors are colorless,” Robinson testified. “The fog-like appearance usually associated with an LNG vapor cloud results from condensation of water vapor in the air due to the lower temperatures of the cloud. However, appearance of this visible water vapor does not necessarily reflect the flammable portion of the cloud.”

He noted that radiant heat generated by a large-scale LNG pool fire is assumed to be greater than heat generated by other common fuels based on small-scale measurements. “However, it has not been proven that this effect would scale up to larger fires,” Robinson testified. “Oxygen deprivation and smoke generation in a larger fire may lead to lower surface emissive power.”

Where FERC is uncertain due to lack of large-scale field data, the Commission model uses conservative assumptions that result in longer hazard distances, he testified. “These conservative assumptions concern: calculation of the pool spread; determination of the pool fire flame height; and use of a higher surface emissive power. Our results have been in agreement with the Sandia guidance zones of concern, and support the conservative nature of the calculations.”

Robinson also provided a review of the FERC’s LNG terminal review procedures and a history of LNG tanker mishaps, none of which resulted in serious leakage of cargo. “Even in the few instances worldwide where there have been incidents, the integrity of LNG vessel construction and safety systems has been demonstrated,” he said.

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